CVS Changes with Obesity

Describe the cardiovascular changes that occur with morbid obesity

Obesity is a multisystem disorder defined by an elevated body mass index (BMI):

  • Normal: BMI < 25
  • Overweight: BMI 25 - 30
  • Obese: BMI > 30
  • Morbidly Obese:
    • Obesity related disease and a BMI > 35
    • BMI > 40

Characteristics of obesity include:

  • Complex genetic and environmental causes
  • Increased caloric intake
  • Increased metabolic rate (normal for BSA)

The effect of obesity on the cardiovascular system is complex, and can be classified into:

  • Hormonal changes
    Abdominal visceral fat is responsible for secreting a large number of hormones which affect cardiovascular parameters:
    • Increased leptin
      Contributes to cardiac remodelling and LVH.
    • Angiotensinogen
      Leads to systemic hypertension and LV remodelling.
      • Small amounts are produced in adipocytes, which increases as fat volume increases
    • Plasminogen activator inhibitor-1
      Reduces fibrinolysis and predisposes to VTE.
    • Inflammatory adipokines
      Impair endothelial function, leading to increased SVR.
    • Catecholamines
      Increased contractility, SVR, and worsen endothelial function.
      • Released with:
        • Hypoxia
        • Hypercapnoea
        • Negative intrathoracic pressure
        • Fragmented sleep
          Due to OSA.
  • Changes in key cardiovascular parameters
    • Increased VO2
      Due to increased LBM and fat mass.
    • Increased Blood Volume
      Due to increased angiotensin II and aldosterone.
    • Increased Stroke Volume
      Due to:
      • Increased preload (major factor)
      • Increased contractility (minor factor)
        Due to increased circulating adrenal hormones.
    • Increased Cardiac Output
      To maintain DO2.
      • Initially with preserved ejection fraction
  • Cardiac changes
    • Diastolic dysfunction
      Due to myocardial fibrosis impairing relaxation.
    • Fatty infiltration of myocardium and conducting system
      • Predisposes to arrhythmias
        Risk is worsened by change in myocardial architecture, hypoxia, and increased circulating catecholamines.
    • Biventricular hypertrophy as a response to increased afterload
      • LV afterload increased due to systemic hypertension
        LVH is much more common than RVH.
        • Eccentric hypertrophy due to volume overload
        • Concentric hypertrophy due to pressure overload or hormonal changes
      • RV hypertrophy due to:
        • LV diastolic failure
        • Increased PVR
          • Hypoxia
            Due to:
            • Effects of OSA
            • Increased shunt through collapsed lung bases
          • Acidosis

References

  1. Alvarez A, Brodsky J, Lemmens H, Morton J. Morbid Obesity: Peri-operative Management. Cambridge: Cambridge University Press. 2010.
  2. Lotia S, Bellamy MC. Anaesthesia and morbid obesity. Contin Educ Anaesth Crit Care Pain 2008; 8 (5): 151-156.
Last updated 2017-09-21

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